Performance limits of amplify-and-forward based fading relay channels

In this paper, we examine the basic building block of cooperative diversity systems, a simple fading relay channel where the source, destination and relay terminals are each equipped with single antenna transceivers. We consider three different TDMA-based cooperative protocols that vary the degree of broadcasting and receive collision. For each protocol, the relay terminal simply amplifies-and-forwards the signal received from the source terminal to the destination. We study the ergodic and outage capacity behavior of each of the protocols assuming Gaussian codebooks and show that full spatial diversity (second-order in this case) is achieved by certain protocols provided that appropriate power control is employed. Finally, we establish the superiority (both from a capacity as well as a diversity point-of-view) of a new protocol proposed in this paper.